Aluminizing Mechanism and Corrosion Resistance of Pipeline Steel X80 by Combined Pack Cementation Process under Low Temperature

In order to improve the corrosion resistance of pipeline steel X80 and maintain its good mechanical properties simultaneously, a low-temperature pack aluminizing process was carried out at 723 K on pipeline steel X80 after a surface mechanical attrition treatment (SMAT). The phase composition, microstructure and element distribution of the as-aluminized pipeline steel X80 were characterized by XRD, SEM and EDS, respectively. The results show that the as-received aluminide layer consists of Fe2Al5, which exhibits a good cohesion with SMATed pipeline steel X80 substrate with the thickness of around 90 mu m. The element concentrations of Al and Fe atoms show a gradual change in the range of aluminide layer. After corrosion test processed in 3.5% NaCl solution, there is no obvious corrosion crack or uphills piled up by corrosion products on the surface of as-aluminized SMATed pipeline steel, which can conclude that pack aluminizing assisting by SMAT at low-temperature is an effective way for protecting pipeline steel X80 against corrosion.